Fats and oils are the most commonly occurring lipids and are a major source of dietary energy. Fats and oils aid in making both natural and prepared food more palatable by improving the texture and by providing a more desirable flavor.
Fats and oils are triacylglycerides or triglycerides formed from the reaction of fatty acids with glycerol as follows: ##STR1## where Z is an organic radical containing about 2 to 24 carbon atoms. The distinction between a fat and an oil is arbitrary. At room temperature a fat is a solid and an oil is liquid. The physical characteristics of fat depend on the distribution of fatty acids on the triglyceride molecules.
Metabolically, ingested triglycerides are hydrolyzed in the small intestines to 2-monoacylglycerides and fatty acids which are then reesterified to triglycerides in the enterocyte of the intestinal wall, absorbed into the blood, and transported In chylomicron vesicles. The body utilizes these triglycerides to form other lipid compounds such as eicosenoids and cholesterol esters, or as a source of energy.
The effects of dietary fatty acids on cholesterol metabolism is of particular interest due to reports which link high levels of cholesterol in the blood (hypercholesterolemia) with arterial disease. Many authorities consider elevated plasma cholesterol a major risk factor in cardiovascular disease.
Low fat diets have long been known to be an effective means for lowering the plasma cholesterol level in humans, and thereby lowering the risk of hypercholesterolemia (Keys et al., Science 112 (1950) 79). Further, research has suggested that the quality of ingested fats influences serum-cholesterol levels. For example, the intake of saturated fatty acids containing 12 to 16 carbon atoms produced increased serum choiesterol levels in humans, whereas, unsaturated fatty acids were found to lower serum cholesterol levels (Keys et al., Metabolism 14 (1965) 747).
Saturated fatty acids (SAFA) from animal fats and plant sources and trans fatty acids (TFA) from partially hydrogenated vegetable oils are routinely used in food products because of their high melting points. The partial hydrogenation of vegetable oils has been the preferred method for developing fats with sufficient hardening characteristics and desired functionalities for use in shortenings, margarines, and other food compositions. Nutritional studies have suggested that TFA from partially hydrogenated vegetable oils may raise LDL-cholesterol to a similar degree as C12:0 to C16:0 fatty acids, whereas stearic acid (C18:0), cis-monounsaturated fatty acids (e.g., oleic acid), and cis-polyunsaturated fatty acids (e.g., linoleic acid) do not. See, for example, Hegsted et al., Amer. J. Clin. Nutr. 17 (1965) 281; Derr et al., Metabolism 42 (1993) 130; Mensink et al., N. Eng. J. Med. 323 (1990) 439.
Efforts have been made to provide fat compositions that balance the desire for lower saturated fat and low trans fatty acids with the need to provide compositions with acceptable physical properties. Current lipid-based technologies for replacing trans fatty acids typically involve the use of saturated fats and hydrogenation in order to attain desired characteristics. For example, U.S. Pat. No. 4,610,899 to Schmidt describes fat blends having relatively low levels of trans fatty acids. However, these fats were produced by random interesterification of lauric fats, saturated fats and a minor proportion of partially hydrogenated fats. The use of asymmetric monounsaturated fatty acids (AMUFAs) to provide a solid edible fat low in saturated fat and free of trans fatty acids is not described.